The objective of this proposed effort is to develop and evaluate high- powered interstitial ultrasound applicator technology and support systems specifically for thermal ablation of liver tumors. Recent investigations with interstitial ultrasound applicators in prostate and moderately perfused tissues have demonstrated extremely controllable and penetrating heating patterns which can be shaped and dynamically altered, providing an ideal mechanism for conformable thermal surgery. In order to extend this technology to liver ablation, the following Phase I studies are proposed: (1) modify existing applicator technology for high- power devices required for liver tumor ablation; (2) perform theoretical investigations of new power application schemes and design parameters specific to ablating liver tumors; (3) develop and integrate system hardware and software for a controlling system prototype; and (4) perform in vivo liver experiments to evaluate applicators and support systems. The feasibility of controlled/conformal treatment of transversely and longitudinally larger tumor volumes in shorter time frames and with greater control will be assessed as compared to existing RF, Laser, and Microwave technology. The results and experience obtained from these studies will be applied to the conceptual development of clinical approaches and procedures in the treatment of liver tumors, with proposed implementation in the succeeding Phase II application. PROPOSED COMMERCIAL APPLICATIONS: Minimally-invasive thermal ablation of liver tumors is a clinically viable technique which provides a less morbid alternative to surgery, and can be applied in patients whose disease is not surgically resectable or are a poor risk for open surgery. Current technology is limited to treating spherically shaped tumors <3cm effectively. High-power interstitial ultrasound technology has significant potential to treat larger tumors of complex shapes in controllable and faster manner, permitting more effective treatment for larger number of cases.